Heretofore, there have been PLC (programmable controller) systems that include a CPU unit (a unit that executes a ladder program) and a positioning device that receives a positioning start instruction from the CPU unit and supplies positioning instruction data to a drive unit. In the positioning devices of PLC systems, a delay time (positioning start time) occurs until a positioning instruction (such as an instruction made by outputting a pulse or by communication) is started with respect to the drive unit, such as a servo amplifier, after a positioning start instruction is received from the CPU unit. This delay time is the data analysis time for generating positioning instruction data by executing a predetermined analytical computation upon receiving the positioning start instruction. In a positioning device having various positioning functions, the number of parameters is large and thus it takes a long time to analyze data; therefore, the positioning start time tends to be long.
There is a description in Patent Literature 1 of an industrial robot control device that sequentially analyzes and executes a plurality of instructions of a program, where the operating environment corresponding to an operation instruction is stored in time series in the time-series data memory when an operation of the motion controller is performed and, when a robot operation that has been suspended is resumed, the operation instruction that was being executed when the robot operation was suspended is read from the time-series data memory and is executed again. Thus, according to Patent Literature 1, it is possible to solve a problem that a robot operation is resumed by executing from the operation instruction next to the operation instruction that was being executed; therefore, the robot operation can be performed as was intended by the program.
Patent Literature 2 describes that the cam operation is reproduced by the feed operation of the motor shaft. Specifically, a data column of time-series instruction positions, each including the amount of correction, such as the delay in the servo system and the lost motion in the mechanical system, is stored in advance in each of the forward operation data table and the backward operation data table, the motor shaft is operated in the forward direction by generating a movement instruction by reading binary data directly from the forward operation data table, and the motor shaft is operated in the backward direction by generating a movement instruction by reading binary data directly from the backward operation data table, thereby performing a binary operation. Therefore, according to Patent Literature 2, even if the operation direction of the shaft is reversed a number of times during the binary operation, an inadvertent delay due to the effect of the delay in the servo system, the lost motion in the mechanical system, and the like is prevented.